Temperature preference and respiration of acaridid mites

The thermal preferences in a grain mass and respiration at various temperatures in mites (Acari: Acarididae) of medical and economical importance [Acarus siro (L. 1758), Dermatophagoides farinae Hughes 1961, Lepidoglyphus destructor (Schrank 1871), and Tyrophagus putrescentiae (Schrank 1781)] were studied under laboratory conditions. Based on the distribution of mites in wheat, Triticum aestivum L., grain along a thermal gradient from 10 to 40 degrees C, L. destructor, D. farinae, and A. siro were classified as eurythermic and T. putrescentiae as stenothermic. The lowest preferred temperature was found for D. farinae (28 degrees C), followed by A. siro (28.5 degrees C), L. destructor (29.5 degrees C), and T. putrescentiae (31.5 degrees C). The relationship between the respiration rate and the temperature was similar for all four mite species. The highest respiration was found in the range from 31 to 33 degrees C. This is approximately 2 degrees C higher than the preferred temperature of these species. The lower temperature threshold of respiration ranged from 1 to 5 degrees C and the upper threshold ranged from 45 to 48 degrees C. Acclimatization of A. siro to temperature regimes of 5, 15, and 35 degrees C resulted in thermal preferences between 9 and 12 degrees C, 9 and 20 degrees C, and 28 and 35 degrees C, respectively. The respiration rate of acclimatized specimens increased with the temperature, reaching a maximum at 29.0 degrees C for mites acclimatized at 5 and 15 degrees C and a maximum at 33.7 degrees C for those acclimatized at 30 degrees C.     

Differential levels of mite infestation of wheat and barley in Czech grain stores

Abstract  While mites are able to utilize numerous food sources, the suitability of the food strongly influences population growth. The different suitabilities of various stored agricultural products will thus affect the level of infestation. In this study, we compared field mite infestation rates in two stored cereals: wheat and barley. We analyzed mite abundance, frequency and species composition in samples of grain obtained from 79 selected Czech grain stores. Stored barley seemed to be more vulnerable to mite attack than wheat, as we consistently found more infested samples, more species and higher mean and median mite abundance per sample in barley as compared to wheat. The mean mite abundance per sample were 55 and 506 individuals for wheat and barley, respectively. In barley, 10% of samples exceeded allergen risk threshold (i.e., 1 000 individuals per kg of grain). Altogether, 25 species were identified from approximately 35 000 individuals. The most frequently identified species were the same in wheat and barley, that is, Tydeus interruptus Sig Thor, Acarus siro L., Tarsonemus granarius Lindquist, Lepidoglyphus destructor (Schrank) and Tyrophagus putrescentiae (Schrank). Based on principal components analysis, we found a closer association of T. interruptus , T. putrescentiae , L. destructor and Cheyletus eruditus (Schrank) with barley samples, corresponding to the high frequency and abundance values of these mites. The probable reasons for the higher infestation, especially mite abundance in barley, are discussed in relation to the higher proportion of crushed parts, which may release favorable nutrient sources and amplify the abundance values.     

The effect of modified atmospheres on the survival of the eggs of four storage mite species

The results of a laboratory investigation into the effects of modified atmospheres (MA) on the eggs of mite pests of grain and cheese are presented. Four species of astigmatid mite were tested; Acarus farris (Oudemans). A. siro L., Lepidoglyphus destructor (Schrank) and Tyrophagus longior (Gervais). All are found in many habitats including grain and cheese stores. Three low oxygen (O2) MA mixtures were used, based on carbon dioxide (CO2), nitrogen (N2) or simulated burner gas (0.5 or 2% O2, 10% CO2, balance N2) plus 60% CO2 in air (8% O2). The mites were exposed at 15 degrees C and 80% r.h., a combination of conditions that occurs at the surface of stored grain during the autumn which promotes mite population growth. The exposure periods required to prevent egg hatch for each species in every mixture are given. Tyrophagus longior was the most tolerant species, followed by A. siro and A. farris, with L. destructor the most susceptible. Burner gas was the most effective mixture overall with 0.5% O2 but with an increase in the O2 level to 2% for all the mixtures, CO2 became the more effective control agent. With 60% CO2 in air some loss of efficacy was observed against the three most tolerant species and even more so for L. destructor. Sublethal exposures to MAs for at least 4 days in L. destructor, 6 days in A. farris and A. siro and 8 days for T. longior caused a delay in egg hatch.     

Spatiotemporal distribution of insects and mites in horizontally stored wheat

Samples were taken from a flat storage facility located in central Greece, filled with approximately 45 tons of hard wheat, to assess the spatiotemporal distribution of stored-product insects and mites. The wheat was stored in a 1.5-m-deep bulk from June 2001 until March 2002. The samples were taken with a partitioned grain trier during the entire storage period, at 10-d intervals. The trier samples were examined separately for the upper, medial, and lower 0.5 m of the bulk. The spatial distribution of the insect and mite species found was examined by contour analysis based on the numbers of individuals in the trier samples. Nine insect and 20 mite taxa were found during the sampling period. The most abundant insect species were Tribolium castaneum (Herbst), Cryptolestes ferrugineus (Stephens), and Rhyzopertha dominica (F.); the most abundant mite species were Lepidoglyphus destructor (Schrank), Acarus siro L., and the predator Cheyletus malaccensis Oudemans. The highest population densities for the majority of the insect and mite species were recorded during autumn. The majority of the individuals of the most abundant insect and mite species were found in the upper 0.5 m of the bulk, with the exception of C. malaccensis, which was equally distributed in the upper and medial 0.5 m of the bulk. The spatiotemporal distribution during the entire experimental period was notably varied according to the insect and mite species.     

OBSERVATIONS ON THE CONTROL OF MITE INFESTATIONS IN STORED WHEAT BY CHEYLETUS SPP. (ACARINA, CHEYLETIDAE)

An account is given of the control of the grain mite Acarus siro L. (= Tyroglyphus farinae L.) by the predatory mite Cheyletus sp. in imported wheat stored in bags or in bulk. After 12–18 months of storage Cheyletus sp. had developed in 75% of the parcels of wheat and in 67% of these it became dominant over other mites. This usually occurred in late summer for bagged wheat. Control of A. siro by Cheyletus sp. compared favourably with that achieved by fumigation with methyl bromide and on occasion was superior. Both development and dominance of Cheyletus sp. were adversely affected by earlier fumigation but there was some evidence that spraying wheat with γ-BHC favoured the development of this species and, in some circumstances, its dominance. Dominance by Cheyletus sp. in bulk grain often occurred in the winter months when the surface moisture content of the wheat was at its highest.
The development of Cheyletus eruditus Schr. is described in a bulk grain store where dense populations of A. siro and Glycyphagus destructor Schr. were eliminated by the predator. The numbers of C. eruditus in wheat tended to increase faster when the surface layers were disturbed than when the grain was undisturbed. Nevertheless, dominance over the other mites tended to occur first in undisturbed grain.     

Detection and identification of species-specific bacteria associated with synanthropic mites

Internal bacterial communities of synanthropic mites Acarus siro, Dermatophagoides farinae, Lepidoglyphus destructor, and Tyrophagus putrescentiae (Acari: Astigmata) were analyzed by culturing and culture-independent approaches from specimens obtained from laboratory colonies. Homogenates of surface-sterilized mites were used for cultivation on non-selective agar and DNA extraction. Isolated bacteria were identified by sequencing of the 16S rRNA gene. PCR amplified 16S rRNA genes were analyzed by terminal restriction fragment length polymorphism analysis (T-RFLP) and cloning sequencing. Fluorescence in situ hybridization using universal bacterial probes was used for direct bacterial localization. T-RFLP analysis of 16S rRNA gene revealed distinct species-specific bacterial communities. The results were further confirmed by cloning and sequencing (284 clones). L. destructor and D. farinae showed more diverse communities then A. siro and T. putrescentiae. In the cultivated part of the community, the mean CFUs from four mite species ranged from 5.2?×?10(2) to 1.4?×?10(3) per mite. D. farinae had significantly higher CFUs than the other species. Bacteria were located in the digestive and reproductive tract, parenchymatical tissue, and in bacteriocytes. Among the clones, Bartonella-like bacteria occurring in A. siro and T. putresecentiae represented a distinct group related to Bartonellaceae and to Bartonella-like symbionts of ants. The clones of high similarity to Xenorhabdus cabanillasii were found in L. destructor and D. farinae, and one clone related to Photorhabdus temperata in A. siro. Members of Sphingobacteriales cloned from D. farinae and A. siro clustered with the sequences of "Candidatus Cardinium hertigii" and as a separate novel cluster.     

Rapid method for the detection of storage mites in cereals: feasibility of an ELISA based approach

This paper describes the development of rapid immunodiagnostic tests for the detection of storage mite infestations in cereals and cereal products. The study's first phase (proof of concept) involved the production of a species-specific enzyme-linked immunoassay (ELISA) for the flour mite, Acarus siro (L.), a major pest of stored commodities. The specificity of this new assay was assessed against key stored product contaminants (13 species of mites of which three were predatory, five species of insects and five species of fungi) in the presence and absence of grain. The assay was species-specific (no cross-reactivity to other storage contaminants) and was unaffected by the presence of cereal antigens in the extract. In the study's second phase, species- and genera-specific ELISAs were developed for a range of key storage mite pests: the cosmopolitan food mite (Lepidoglyphus destructor), the grocers' itch mite (Glycyphagus domesticus), the grainstack mite (Tyrophagus longior), mites of the Tyrophagus and Glycyphagus generas, and all storage mites. All tests were demonstrably specific to target species or genera, with no cross-reactions observed to other storage pest contaminants or cereals. The final, validation phase, involved a comparative assessment of the species-specific A. siro and the genus-specific Tyrophagus ELISAs with the flotation technique using laboratory and field samples. Both ELISAs were quantitative (0-30 mites per 10 g wheat) and produced good comparative data with the flotation technique (A. siro r(2)=0.91, Tyrophagus spp. r(2)=0.99).     

Molecular and biochemical properties of storage mites (except Blomia species)

In recent years, the allergological importance of different mite species not belonging to the family Pyroglyphidae has been demonstrated. These mites, commonly named storage mites, include Lepidoglyphus destructor, Glycyphagus domesticus, Tyrophagus putrescentiae, Acarus siro, Aleuroglyphus ovatus, Suidasia medanensis and Thyreophagus entomophagus. Several allergens from these species have been purified, sequenced and cloned. Many of these allergens have shown sequence homology and a biological function similar to those previously described in Blomia tropicalis and the Dermatophagoides spp. The main allergens described in storage mites include fatty acid binding proteins, tropomysin and paramyosin homologues, apoliphorine like proteins, alfa-tubulines and other, such as group 2, 5 and 7 allergens, which definitive biological function has not been described yet. Besides the purification and characterization of allergens, the allergenicity of other species such as Acarus farris, Austroglycyphagus malaysiensis, Blomia kulagini and B. tjibodas, Cheyletus eruditus, Chortoglyphus arcuatus, Gohieria fusca, Thyreophagus entomophagus and Tyrophagus longior has been investigated. Research has also been conducted to identify allergens in parasitic mites, such as Psoroptes ovis, Sarcoptes scabiei, Varroa jacobsoni, Diplaegidia columbae and Hemisarcoptes cooremani. The allergenicity of mites present in agricultural environments has been investigated. Crossreactivity studies have also been performed to elucidate to what extent all these mites share common, or species specific epitopes. Herein we present a comprehensive review of the allergenicity of mite species which have been implicated in human respiratory and/or dermatological diseases.     

The efficacy of Dryacide, an inert dust, against two species of Astigmatid mites, Glycyphagus destructor and Acarus siro, at nine temperature and moisture content combinations on stored grain

Dryacide, an inert silicaceous dust, was tested for efficacy on wheat after 14 and 28 days exposure against the mites Acarus siro and Glycyphagus destructor at doses of 1, 3 and 5 g kg–1, moisture contents (MCs) of 14.5, 15.5 and 16.5% and temperatures of 10, 17.5 and 25°C. After 28 days at 10°C, all doses were effective against A. siro with the exception of the lowest dose at the highest MC, but against G. destructor complete control only occurred at 3 g kg–1 and 14.5% MC and at 5 g kg–1 and 14.5 and 15.5% MC. After 28 days at 17.5°C, the dust was fully effective against A. siro at 3 and 5 g kg–1 but only at 14.5% MC. Glycyphagus destructor was only completely controlled after 28 days at 5 g kg–1 and 14.5% MC. After 14 days at 25°C, A. siro was completely controlled at 3 and 5 g kg1 and 14.5% MC as was G. destructor after 28 days. Neither species appeared to ingest the dust but considerable quantities adhered to their cuticles. The high mortalities observed under the range of experimental conditions, particularly the lowest temperature, suggest that a dose of 3 g kg–1 may be effective as a replacement for organo-phosphorous (OP) pesticide surface treatments in an integrated storage strategy based on grain cooling. © Rapid Science Ltd. 1998     

Acaricidal effect of a diatomaceous earth formulation against Tyrophagus putrescentiae (Astigmata: Acaridae) and its predator Cheyletus malaccensis (Prostigmata: Cheyletidae) in four grain commodities

Laboratory bioassays were conducted to evaluate the effect of the diatomaceous earth (DE) formulation SilicoSec (Biofa GmbH, Münsingen, Germany), against two stored-product mite species, Tyrophagus putrescentiae (Shrank) and the predator Cheyletus malaccensis Oudemans. For this purpose, DE was applied in wheat, oat, rye, and maize, at the dose rates 0, 0.5, 1, and 2 g/kg grain. The mortality of the exposed mites was assessed after 24 h, 48 h, 7 d, and 14 d of exposure in the treated substrate. After this interval, the treated grains were checked for oviposition or progeny. The tests were conducted at 80% RH and at two temperatures, 20 and 25 degrees C. Generally, for both species, mortality was higher at 25 degrees C than at 20 degrees C. For T. putrescentiae, at both temperatures, the mortality in grains treated with the highest DE rate was 100% after only 24 h of exposure, with the exception of maize at 20 degrees C, where mortality was 91.7%. The mortality of C. malaccensis after 24 h of exposure to the treated grains, in the absence of prey, did not exceed 29% at any of the temperature- grain-dose combinations, whereas no mites were dead in rye and maize treated with 0.5 and 1 g of DE. Even after 14 d of exposure at the highest DE rate, mite mortality did not reach 100%. The presence of T. putrescentiae individuals as prey in the treated substrate enhanced C. malaccensis survival. Hence, after 14 d of exposure, the mortality of C. malaccensis, in wheat, oat, rye, and maize treated with the highest DE rate was 51.7, 59.7, 70, and 36.9, respectively. No progeny production was recorded in the treated substrate for T. putrescentiae; in contrast, oviposition and F1 progeny were recorded for C. malaccensis. Our results suggest that the use of C. malaccensis with low doses of DE may be an appealing integrated pest management (IPM) approach against T. putrescentiae, and probably against other stored-grain mite species.     

Mites and fungi in heavily infested stores in the Czech Republic

Toxigenic and allergen-producing fungi represent a serious hazard to human food and animal feed safety. Ninety-four fungal species were isolated from mite-infested samples of seeds taken from Czech seed stores. Fungi were isolated from the surface of four kinds of seeds (wheat, poppy, lettuce, and mustard) and from the gut and external surface of five species of mites (i.e., Acarus siro L., 1758, Caloglyphus rhizoglyphoides (Zachvatkin, 1973), Lepidoglyphus destructor (Schrank, 1781), Tyrophagus putrescentnae (Schrank, 1781) and Cheyletus malaccensis Oudemans 1903) separately. Multivariate analysis of fungi complex composition showed that the frequency of fungal was species significantly influenced by the kind of seed. Fungal frequencies differed between mites gut and exoskeleton surface and between the surfaces of mites and seeds. Three groups of fungal species were recognized: 1) mite surface-associated fungi: Penicillium brevicompactum, Alternaria alternata, and Aspergillus versicolor; 2) mite surface- and seed-associated fungi: Aspergillus niger, Penicillium crustosum, Penicillium aurantiogriseum, Penicillium chrysogenum, and Aspergillus flavus; and 3) seed-associated fungi: Cladosporium herbarum, Mucor dimorphosporus f. dimorphosporus, Botrytis cinerea, Penicillium griseofulvum, and Eurotium repens. Mite-carried species of microfungi are known to produce serious mycotoxins (e.g., aflatoxin B1, cyclopiazonic acid, sterigmatocystin, ochratoxin A, and nephrotoxic glycopeptides) as well as allergen producers (e.g., A. alternata and P. brevicompactum). Storage mites may play an important role in the spread of some medically hazardous micromycetes. In addition, these mite-fungi associations may heighten the risk of occurrence of mycotoxins in food and feed stuffs and cause mixed contamination by fungal and mite allergens.     

The effectiveness of organophosphate acaricides on stored product mites interacting in biological control

Three organophosphates (pirimiphos-methyl, chlorpyrifos-methyl, chlorpyrifos) were tested on a laboratory strain of Cheyletus eruditus (Schrank), a predatory mite used for biological control of stored food mites, and on tow species of acaroid mites, Acarus siro L. and Tyrophagus putrescentiae (Schrank). Biological control is often preceded by a chemical treatment with organophosphates and thus it is important to know how the acaricides affect the predators. It was found that chlorpyrifos-methyl was the most toxic organophosphate on C. eruditus. The effectiveness of pirimiphos-methyl and chlorpyrifos was approximately equal and was three times lower than the effectiveness of chlorpyrifos-methyl. The organophosphates were nearly equally effective on both acaroid mites but A. siro was slightly more susceptible than T. putrescentiae. On the basis of these results, the use of pirimiphos-methyl or chlorpyrifos rather than chlorpyrifos-methyl is recommended for protection of empty stores or stored grain against resiliant populations of stored food mites.     

Spatial associations of insects and mites in stored wheat

The spatial association pattern of insect and mite populations in a steel bin containing stored wheat, Triticum durum Desf., in central Greece, was studied using the Spatial Analysis by Distance IndicEs (SADIE). The monitoring was carried out for 7 mo by using grain trier samples and probe traps. The most abundant insect species were Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). For mites, the most abundant species were the phytophagous Lepidoglyphus destructor (Schrank) (Acari: Glycyphagidae) and the predator Blattisocius tarsalis (Berlese) (Mesostigmata: Ascidae). Both for P. interpunctella and C. ferrugineus, trap catches were associated with numbers of individuals in the trier samples, but the overall association index calculated among trap and sample counts was significant only in the 33% of trap-sample pairs of values. Generally, P. interpunctella had the main patch areas in the central part of the bin, with few exceptions, during the entire monitoring period. Similar trends also were noted in the case of C. ferrugineus, which was clearly aggregated in the center of the grain mass. Spatial association maps indicated a stable positive association in the central part of the bin, but in most of the other sampling zones the association was negative. However, distribution of L. destructor, based on trier samples, indicated increased presence in peripheral zones of the grain sampling area. Moreover, B. tarsalis presented the most dispersed distribution among all four species. For each species, the association between two consecutive samplings was significant in the majority of cases, indicating a stable spatial pattern. Finally, B. tarsalis was spatially associated to a higher degree with the insects found rather than with L. desctructor. Moreover, there was no association of insect and mite presence with grain temperature and moisture content. The results of the current study suggest that the coexistence of insects and mites in bulked grain follows a complex pattern, with significant interactions, especially in the case of mite predators, which are spatially associated with insect species.     

The influence of temperature and relative humidity on the development of Lepidoglyphus destructor (Acari: Glycyphagidae) and its production of allergens: a laboratory experiment

Laboratory experiments with Lepidoglyphus destructor on a diet of mainly whole wheat were conducted to study the mite's development and production of a specific allergen, Lep d 2, at four different temperatures (5, 10, 15 and 20 degrees C) and three levels of relative humidity (ca. 70-88%). Statistical models were used to analyse the role played by temperature, relative humidity and time in explaining the observed number of L. destructor and the amount of allergen produced. Moreover, the life stage distributions of the mites were determined and related to the population growth. Based on a statistical model the intrinsic rate of natural increase, rm, was computed for a range of different temperatures and relative humidities. High relative humidity in combination with temperatures at about 25 degrees C will lead to the highest rm (ca. 0.15 day-1). The highest concentration of Lep d 2 was 3 micrograms g-1 grain, found at 20 degrees C and high relative humidity at a mite density of 254 mites g-1 grain. The concentration of allergens in the grain was best explained by a model that incorporated both the current and the cumulative numbers of mites.     

Chitin in the peritrophic membrane of Acarus siro (Acari: Acaridae) as a target for novel acaricides

The peritrophic membrane in Acarus siro L. (Acari: Acaridae) is produced by distinct cells located in the ventriculus. In this study, the chitin inside the peritrophic membrane was detected using wheat germ-lectin conjugated with colloidal gold (10 nm). The chitin fibrils of the peritrophic membrane were a target for chitin effectors, including 1) chitinase, which hydrolyzes chitin fibers inside the peritrophic membrane; 2) calcofluor, which binds to chitin and destroys the peritrophic membrane mesh structure; and 3) diflubenzuron, which inhibits chitin synthesis. In addition, soybean trypsin protease inhibitor (STI) and cocktails of chitinase/calcofluor, diflubenzuron/calcofluor and chitinase/STI were tested. These compounds were supplemented in diets and an increase of population initiated from 50 individuals was observed after 21 d of cultivation. Final A. siro densities on experimental and control diets were compared. The chitin in the peritrophic membrane was determined to be a suitable target for novel acaricidal compounds for suppressing the population growth of A. siro. The most effective compounds were calcofluor and diflubenzuron, whereas the suppressive effects of chitinase and STI were low. The failure of chitinase could be due to its degradation by endogenous proteases. The combination of chitinase and STI suppressed A. siro population growth more effectively than when they were tested in oral admission separately. The combinations of calcofluor/chitinase or calcofluor/difluorbenzuron showed no additive effects on final A. siro density. The presence of chitin in peritrophic membrane provides a target for novel acaricidal compounds, which disrupt peritrophic membrane structure. The suitability of chitin effectors and their practical application in the management of stored product mites is discussed.     

The efficacy of four avermectins on the synanthropic mite Lepidoglyphus destructor under laboratory conditions

The effect of four avermectins on the population growth of pest mite Lepidoglyphus destructor was tested in laboratory experiments. The avermectins (abamectin, doramectin, emamectin-benzoate and ivermectin) of analytical purity were incorporated into an experimental diet at the same molar concentrations, ranging from 0.16 to 8 nmol/3 g of diet. Using an initial population of 50 mites, the population growth was recorded after 21 days at 85 % relative humidity and 25 °C; 12 repeats were performed per avermectin concentration and control. The diets containing the avermectins successfully suppressed the population growth of L. destructor. The EC(50) recalculated to ng of substance per g of diet showed different suppressive effects of the avermectins: doramectin (181 ng/g diet), abamectin (299 ng/g diet), emamectin-benzoate (812 ng/g diet) and ivermectin (992 ng/g diet). Of the tested avermectins, abamectin is registered for the control of phytophagous mites and ivermectin against parasitic mites, i.e., Psoroptes ovis. Although emamectin-benzoate and ivermectin were less effective on L. destructor, all of the tested avermectins are highly suitable compounds for the control of synanthropic mites.     

Impact of wheat-mung bean intercropping on English grain aphid (Hemiptera: Aphididae) populations and its natural enemy

The effects of intercropping wheat, Triticum aestivum L., with mung bean, Vigna radiate L., on the populations of English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), and its natural enemies were evaluated by field and laboratory experiments. The population densities of aphids and their natural enemies were evaluated in the intercropped field against different row ratio combinations of wheat-mung bean. Results showed that wheat-mung bean intercropping caused a drop in aphid densities, and the ratio 12 wheat: 4 mung bean brought about the largest drop (> 8%). In addition, the population densities of coccinellids (ladybirds) and parasitoids and the species diversity of all the natural enemies of aphid were higher in the intercropped field than in the field planted only with wheat. However, intercropping did not influence the community indices (evenness and index of dominance concentration) of the natural enemies. Y-tube olfactometer bioassays were carried out in the laboratory to test whether odor blends of host and nonhost plants affect the host selection of S. avenae. Bioassays indicated that both apterous and alate aphids significantly preferred host plant odor over odor blends of host and intercropped species. Hence, the olfactory-based host location of aphids in the field might be affected by intercropping. The intercropping experiment clearly showed that increased crop species diversity suppresses aphid population growth and preserves the population of natural enemies of aphids. Our results also provide support for the "resource concentration hypothesis" and the "enemies hypothesis".     

Comparative analyses of proteolytic activities in seven species of synanthropic acaridid mites

Microplate assays with 96 wells were optimized to screen proteolytic activities in mite homogenates. Whole-mite extracts of Acarus siro, Aleuroglyphus ovatus, Tyrophagus putrescentiae, Tyroborus lini, Carpoglyphus lactis, Lepidoglyphus destructor, and Dermatophagoides farinae exhibited non-specific proteolytic activity in buffers from pH 2 to 12, and three peaks of highest activity at pH 3, 5-6, and 10 were distinguished. The reducing agent Tris(2-carboxyethyl)phosphine hydrochloride decreased general proteolytic activity on azocasein at pH 5 and 6. The results obtained on two non-specific substrates, azocasein and azoalbumin, showed highly different ranks of the species at pH 5 and 6. Proteolytic activities toward N(α)-Benzoyl-D,L-arginine 4-nitroanilide hydrochloride, N-Succinyl-L-alanyl-L-alanyl-L-prolyl-L-phenylalanine 4-nitroanilide, N-Succinyl-L-alanyl-L-alanyl-L-alanine 4-nitroanilide, Benzyloxycarbonyl-L-arginine-L-arginyl 4-nitroanilide, and N-Methoxysuccinyl-L-alanyl-L-alanyl-L-prolyl-L-methionine 4-nitroanilide (MAAPMpNA) were highest at alkaline pH, but the activity toward MAAPMpNA was also high at pH 5 and 6. In contrast, N-Succinyl-L-alanyl-L-alanyl-L-phenylalanine 4-nitroanilide (AAPpNA) and L-arginyl 4-nitroanilide (ArgpNA) had the highest activity recorded at pH 6. The high activities observed on AAPpNA, ArgpNA, and MAAPMpNA at digestive pH suggest that enzymes present in these extracts could have the majority of proteolysis in the mite gut. Evidence of the presence of proteolytic activities on all tested substrates and in all the tested mite homogenates suggests that the proteolytic activities may contribute to allergenicity. Poor or undetected hydrolytic activities of mite extracts toward substrates for keratin and collagen at digestive pH underline the importance of ecological interactions between mites and microorganisms in the utilization of such substrates.     

<Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> var. <Emphasis Type="Italic">tenebrionis</Emphasis> control of synanthropic mites (Acari: Acaridida) under laboratory conditions

Bacillus thuringiensis (Bt) toxins present a potential for control of pest mites. Information concerning the effect of Bt and its possible application to the biocontrol of synathropic mites is rare. The toxic effect of Bacillus thuringiensis var. tenebrionis producing Cry3A toxin was tested on the mites Acarus siro L., Tyrophagus putrescentiae (Schrank), Dermatophagoides farinae Hughes, and Lepidoglyphus destructor (Schrank) via feeding tests. Fifty mites were reared on Bt additive diets in concentrations that ranged from 0 to 100 mg g⁻¹ under optimal conditions for their development. After 21 days, the mites were counted and the final populations were analyzed using a polynomial regression model. The Bt diet suppressed population growth of the four mite species. The fitted doses of Bt for 50% suppression of population growth were diets ranging from 25 to 38 mg g⁻¹. There were no remarkable differences among species. Possible applications of Bt for the control of synanthropic mites are discussed.     

Characterization of resistance to three bruchid species (Callosobruchus spp., Coleoptera,Bruchidae) in cultivated rice bean (Vigna umbellata)

Resistance of wild and cultivated rice bean (Vigna umbellata [Thunberg] Ohwi and Ohashi) to three bruchid species, Callosobruchus chinensis L., Callosobruchus maculatus F., and Callosobruchus analis F., was evaluated. All but three accessions of cultivated, and all wild rice bean accessions tested, exhibited complete resistance to all three bruchid species. Rice bean seeds with seed coat removed also showed complete resistance to the three bruchid species. Results indicate that physical attributes and/or chemical(s) present in the seed coat of rice bean are not the main factors responsible for resistance. Feeding tests were performed by using artificial beans prepared with varying proportions of rice bean (resistant) and azuki bean (susceptible) flour. Number of bruchid adults that emerged decreased, and larval developmental period (days) was extended, when artificial beans with an increasing proportion of rice bean flour were used. These tests revealed that a chemical compound(s) contained in the cotyledon of rice bean has an inhibitory effect on the growth of these bruchid species. The results also indicate that the chemical(s) in rice bean cotyledon is most effective against C. maculatus.